The Environmental Protection Laws enacted in the United States decades ago have imposed ever increasing limits on permitted emissions from internal combustion engines. The diesel engine has enjoyed a position of being a durable and fuel efficient engine thus making it the engine of choice for commercial, industrial and agricultural use. As emissions limits have been lowered, it becomes increasingly more difficult to meet the standards with a diesel engine.
The most recent standards require diesel particulate filters (DPF) to remove particulate matter from the exhaust of a diesel engine before it is transmitted to the environment. While these filters do an effective job of removing particulate matter from the exhaust, they require periodic cleaning. This entails increasing the exhaust temperature to around 600° C. at which point the carbon particles trapped by the filter combust and in effect provide a cleaning of the filter. Since the exhaust temperature of a diesel engine is significantly lower than 600° C., owing to its inherent efficiency, means must be provided for temporarily increasing the exhaust temperature. A preferred method for achieving this elevated temperature is to pass hydrocarbons over a catalytic converter to increase the temperature of the exhaust mixture to the required level.
There are two primary approaches to adding necessary hydrocarbons to the exhaust. One method involves utilizing the engine controller to inject excess fuel into the engine cylinder at a time when it will not burn so that the fuel is exhausted with the normal products of combustion and flows to the catalytic converter. While this method provides good mixing of the hydrocarbons and the exhaust stream, it usually promotes undesirable leakage of the fuel into the engine lubricating oil, resulting in adverse consequences.
The second approach for adding hydrocarbons to the exhaust involves injecting a fuel spray into the exhaust flow downstream of the main engine and its immediate components, such as a turbocharger utilized. This approach avoids the problem of fuel dilution in the engine lubricant. However, it creates new problems in that adequate time and distance must be provided to ensure complete mixing of the hydrocarbons in the exhaust stream prior to the time it passes over the catalytic converter. Typically, it is considered that up to one meter in length is needed to permit adequate mixing. In many instances the engine installation is such that one meter of an exhaust line prior to the catalytic converter is extremely difficult to accommodate.
What is needed in the art therefore, is a compact system for adding hydrocarbons to the exhaust stream of an internal combustion engine without the problems of oil dilution.